The invention relates to a magnetic resonance method for two-dimensional or three-dimensional imaging of an examination zone, in k-space is scanned at predetermined sampling positions according to the preamble of claim 1. The invention relates further to a magnetic resonance apparatus according to the preamble of claim 9 and to a computer program product according to the preamble of claim 10.
Normal acquisition schemes for magnetic resonance methods are as an example known from U.S. Pat. No. 5,498,961, which shows in FIG. 4 the progression in time when a plurality of sets of raw data are acquired, the gradient direction being plotted as the ordinate whereas the time is plotted as the abscissa. Each point in the diagram corresponds to the acquisition of a magnetic resonance signal. Since the MR signal per se is acquired during a finite period of time, which is negligibly small in relation to the total acquisition time for a complete set of raw data, a single magnetic resonance signal is symbolized by a point in the diagram. The distance in time between two successive points thus corresponds to the repetition time of the sequence. After a first set of raw data has been acquired in this manner, immediately a further measurement period commences, during which a second set of raw data is acquired, followed by a third set, etc. It is explicitly stated that within a measurement period any order of gradient may be chosen, however, it is necessary that this order in the second and the third measurement period shall be maintained.
On the other hand it is possible to diminish the acquisition time for a set of data by sharing the acquisition data of previous sets or scans, which is generally known as profile sharing. There are different known methods of profile sharing like the so called xe2x80x9ckeyhole methodxe2x80x9d, wherein the central part of the k-space will be acquired more often because dynamics for instance for cardiac MR scans occur more in the central k-profiles. Profile sharing as such is also known under the names GES, FAST CARD, TRICKS etc. The basic principle of these acquisition schemes is that the k-space being divided in segments which are acquired with different frequencies, which acquisition segments will be combined with more often repeated central k-space profiles. In this manner the resolution in time between subsequent images can be improved.
The above mentioned acquisition schemes do have several drawbacks in that these profile sharing scans will only give a satisfactory result for dynamic scans. On the other hand the image data in the outer k-space will be defined once and for all, which may influence the resolution negatively.
It is an object of the present invention to improve the acquisition scheme in profile sharing that faster imaging in magnetic resonance will be available whereas problems like fold-over artefacts and/or ghosting and too low resolution will be suppressed to a great extent. A further object of the present invention is to provide a magnetic resonance apparatus and a computer program product designed for faster imaging while suppressing the forming of fold-over artefacts and/or ghosting.
The first object of the invention is accomplished by a magnetic resonance imaging method as defined in claim 1. The further objects of this invention are accomplished by a magnetic resonance apparatus according to claim 9 and by a computer program product according to claim 10.
The data acquisition according to the present invention has the main advantage that sampling will occur in the region of most interest, i.e where imaging is most important for statements of high relevance and quality. Another import feature of the present invention is that forming of artefacts or ghosting is suppressed to an essential extent.